System for detecting underinflated tire in a rolling vehicle

Abstract

The speeds of two wheels are detected by means of wheel speed transducers associated with each wheel, each producing a DC voltage signal proportional to the respective wheel speed. The circuit includes two electric comparators, each having two inputs and one output, each output controlling a fault indicator in the form of an incandescent light. The two inputs for each comparator are the two produced DC voltage signals; and each comparator is identified with one transducer which provides a triggering wheel speed signal, with the other transducer providing a reference wheel speed signal. Sensitivity resistors provide a positive bias on the reference signal input to each comparator. Normally the two wheel speed signals are the same; however, when a triggering wheel speed signal increases a selected amount relative to the reference wheel speed signal, responsive to an underinflated tire, the associated comparator switches to activate the fault light to indicate an underinflated tire.

What is claimed is: 
     
       1. An advisory system for detecting and indicating immediately a selected difference in rotational speed of a pair of load bearing wheels of a vehicle comprising first and second signal generating means associated respectively with first and second vehicle wheels, each including wheel speed transducer means coupled to a wheel, for producing a continuous DC voltage wheel speed signal which is proportional in linear relation to the rotational speed of the wheel;   electric comparator means for producing an output signal responsive immediately to a selected difference between two DC voltage input signals applied thereto;   electrically operated fault signaling means responsive to an output signal from said comparator means;   means applying as input signals to said comparator means a first DC voltage wheel speed signal generated by said first signal generating means, and a second DC voltage wheel speed signal generated by said second signal generating means; said comparator means producing an output signal to activate said fault signaling means, when one of said wheel speed signals changes by a selected DC voltage increment relative to the other of said wheel speed signals, said one wheel speed signal functioning as a triggering signal and said other wheel speed signal functioning as a reference signal.   
     
     
       2. An advisory system a set forth in claim 1 each of said wheel speed transducer means comprising an electrically energized magnetic circuit which generates a pulsating voltage signal proportional to wheel speed; and said signal generating means including amplifier means for converting said pulsating voltage signal to a relatively smooth DC voltage signal.   
     
     
       3. An advisory system as set forth in claim 2 said transducer means generating a pulsating signal having a frequency of about 50 cycles per wheel revolution, to enable production of a very smooth DC voltage signal by said amplifier means.   
     
     
       4. An advisory system as set forth in claim 2 each of said amplifier means including an integrating stage; and said integrating stages for both said amplifier means being carried on a common integrated circuit component, to provide for temperature tracking of said two amplifier means.   
     
     
       5. An advisory system as set forth in claim 1 said comparator means producing an output signal to activate said fault signaling means when said triggering wheel speed signal increases a selected amount relative to its respective reference signal, said triggering signal increase resulting from a faster rolling wheel produced by an underinflated tire having a decreased rolling radius.   
     
     
       6. An advisory system as set forth in claim 1 said electric comparator means comprising first and second separate comparator means;   said fault signaling means being responsive to output signals from either of said comparator means;   means applying, as input signals to said first comparator means, said first and second wheel speed signals, with the first wheel speed signal functioning as said triggering signal and the second wheel speed signal functioning as said reference signal; said first comparator means producing an output signal to activate said fault signaling means when said first wheel speed signal increases a selected amount in relation to said second wheel speed signal;   and means applying, as input signals to said second comparator means, said first and second wheel speed signals, with the first wheel speed signal functioning as said reference signal and the second wheel speed signal functioning as said triggering signal; said second comparator means producing an output signal to activate said fault signaling means when said second wheel speed signal increases a selected amount in relation to said first wheel speed signal.   
     
     
       7. An advisory system as set forth in claim 6 sensitivity resistor means coupling the inputs of said first and second comparator means to said respective reference signal generating means; a source of positive voltage connected to the coupling points of said sensitivity resistor means and respective comparator inputs, and said sensitivity resistor means and said voltage source coacting to produce a positive bias voltage on said reference signal; and said comparator means producing an output signal to activate said fault signaling means when a wheel speed triggering signal goes positive relative to its respective reference signal by the amount of said positive bias voltage.   
     
     
       8. An advisory system as set forth in claim 7 said sensitivity resistor means being readily changeable in said system, to change the positive bias voltage and thereby to change the sensitivity of said system.   
     
     
       9. An advisory system as set forth in claim 6 each of said wheel speed transducer means comprising an electrically energized magnetic circuit which generates a sinuous voltage proportional to wheel speed; and first and second amplifier means coupled to said first and second wheel speed transducer means respectively, for converting said sinuous voltage signal to a relatively smooth DC voltage signal.   
     
     
       10. An advisory system as set forth in claim 6 said vehicle having four wheels including left and right pairs of side-by-side wheels;   said first wheel speed transducer means being associated with one wheel of each of said wheel pairs, and said second wheel speed transducer means being associated with the other wheel of each of said wheel pairs.   
     
     
       11. An advisory system as set forth in claim 6 said vehicle having eight wheels including a plurality of bogies each carrying four wheels; said four wheels of a bogie being arranged in front and rear pairs of side-by-side wheels;   said first and second wheel speed transducer means being associated respectively with diagonally opposite front and rear wheels of one of said bogies.   
     
     
       12. An advisory system as set forth in claim 6 switching means for providing, selectively, energizing voltage for said fault signaling means;   electric comparator means for controlling said switching means;   means applying one of said wheel speed voltage signals as the positive input for said comparator means; means providing a selected positive voltage as the negative input of said comparator means;   said selected negative input voltage for said comparator means being selected to correspond to a wheel speed signal related to a selected vehicle speed, whereby said comparator means will effect the operation of said switching means to remove said energizing voltage for said fault signaling means when said vehicle reaches said selected vehicle speed thereby rendering said system inoperative when said selected vehicle speed is reached.   
     
     
       13. An advisory system a set forth in claim 7 said sensitivity resistor means for each comparator comprising resistor means of different values connected between the respective comparator inputs and the respective wheel speed signal generating means; and switching means for connecting said resistor means alternatively in circuit;   comparator means for controlling said switching means;   means applying one of said wheel speed signals as the input voltage at the negative input of said comparator; and means providing a selected positive voltage to the positive input of said comparator;   said selected voltage applied to the comparator positive input corresponding to a wheel speed signal voltage which relates to a selected speed of said vehicle, whereby said circuit automatically shifts between said sensitivity resistor means of different values at said selected speed of said vehicle.   
     
     
       14. An advisory system as set forth in claim 2 said signal generating means associated with said first wheel comprising a first signal generating channel, and said signal generating means associated with said second wheel comprising a second signal generating channel; said amplifier means for said respective signal generating means including stages for squaring said pulsating voltage signal, for differentiating said squared voltage signal, and for integrating said differentiated signal to produce said relatively smooth DC voltage signal which varies in linear relation with the frequency of said pulsating voltage signal;   said integrating stages for both said channels being carried on a common integrated circuit component.   
     
     
       15. An advisory system as set forth in claim 12 said differentiating stages for both said channels being carried on said common integrated circuit component.   
     
     
       16. An advisory system as set forth in claim 9 said amplifier means including circuit means for amplifying said sinuous voltage signal, circuit means for squaring said amplified sinuous voltage signal; circuit means for differentiating said squared voltage signal; and circuit means for integrating said differentiated voltage signal to produce said relatively smooth DC voltage signal which varies in linear relation with said sinuous voltage signal.   
     
     
       17. An advisory system as set forth in claim 16 said integrating circuit means for both said amplifier means being carried on a common integrated circuit component.   
     
     
       18. An advisory system as set forth in claim 16 said differentiating circuit means and said integrating circuit means for both said amplifier means being carried on a common integrated circuit component.   
     
     
       19. A method for detecting an underinflated load bearing wheel of a vehicle comprising the steps: producing first and second DC voltage signals proportional in amplitude, respectively, to the changing rotational speeds of first and second vehicle wheels;   feeding said first and second DC voltage signals as two inputs to each of independent first and second comparators;   calibrating each of said comparators to produce an output signal when its first input is more positive than its second input;   feeding said first voltage signal as a triggering input to said first comparator, and as a reference input to said second comparator;   feeding said second voltage signal as a triggering input to said second comparator, and as a reference input to said first comparator;   applying a selected positive bias voltage to each of said reference signals, said bias voltage being the equivalent of a wheel speed voltage signal representing the minimum difference in rotational speed to be detected, whereby a triggering signal must exceed its respective reference signal by the magnitude of said bias voltage to produce said comparator output signal;   detecting output signals from said comparators as indications that one vehicle wheel is rotating faster than the other because of relative underinflation of the one wheel; an output signal from said first comparator indicating an increase in rotational speed of, and underinflation of, said first wheel; and an output signal from said second comparator indicating an increase in rotational speed of, an underinflation of, said second wheel.   
     
     
       20. A method as set forth in claim 19 including the step: activating a common fault signal with the outputs of both said comparators; said fault signal indicating underinflation of either one of said vehicle wheels.   
     
     
       21. A method as set forth in claim 19 including the steps producing first and second pulsating voltage signals proportional in frequency, respectively, to the changing rotational speeds of first and second wheels;   and converting said pulsating voltage signals, respectively, to said first and second smooth DC voltage signals which vary linearly with the respective wheel speeds.